1. Field of the Invention
The present invention relates to an image forming apparatus and, more specifically, to an image-transfer device capable of faithfully transferring an image from an image-bearing member to a sheet-like material.
2. Description of the Related Art
An image-transfer device in an image forming apparatus such as an electrophotographic copying apparatus and an electrostatic recording apparatus, as, for example, disclosed in U.S. Pat. No. 5,225,879, has a transfer charger which is a DC corona discharger and a separation charger which is an AC corona discharger. The transfer charger and the separation charger are arranged to be separated from a photoconductive drum which constitutes the image-bearing member. The transfer charger discharges a back surface of a paper sheet via the DC corona to electrostatically transfer a toner image from the photoconductive drum to the paper sheet. Then, the separation charger discharges the paper sheet via the AC corona to electrostatically separate the paper sheet with the toner image, from the photoconductive drum.
In a conventional image-transfer device having the above structure, each output level of the transfer charger and the separation charger is controlled to be constant during the transfer and the separation operations.
However, even if these output levels are controlled to be constant, the toner image transferred onto the sheet paper is not of uniform quality. The toner is somewhat spotty especially in the region of the leading end portion and the trailing end portion of the paper sheet.